Pressure is growing for a public inquiry into a series of deaths of elderly people at a hospital in Gosport, Hampshire, as a doctor faces the General Medical Council charged with giving patients excessive doses of the drug diamorphine.

Jane Barton, who worked with elderly patients at Gosport War Memorial hospital, is alleged to have given excessive, inappropriate and potentially dangerous doses of painkilling drugs including diamorphine and midazolam to 12 patients between January 1996 and November 1999.

Last year, the General Medical Council (GMC) imposed an interim order on ­Barton, the main doctor in charge of two wards at the hospital, prohibiting her from prescribing such drugs to further patients pending the full hearing.

In April this year, more than a decade after the concerns were first raised, an inquest was held into the deaths of 10 of 92 patients at the hospital whose ­relatives had contacted the police with their concerns.

In five of the 10 cases a jury ruled that drugs had contributed to the deaths. In three of the five, the jury said diamorphine had been inappropriately prescribed.

Peter Walsh, of the Association for the Victims of Medical Accidents, a legal group supporting some of the families, said the selection of the 10 patients for inquests had been fairly arbitrary. "It's never been properly explained why [they] were considered and not others," he said.

The fact that diamorphine had been found to be a factor in half the deaths led him to think it could have been involved in other deaths that did not lead to inquests. "I suspect there could have been much more widespread poor practice. We and the families are calling for a public inquiry."

The Portsmouth coroner and Hampshire police have written to the Department of Health saying that a full inquiry would be preferable to a series of inquests.

Norman Lamb, the Liberal Democrats' health spokesman, is backing the families' case. "The families have an understandable sense of having been ignored for years and they have been hitting their heads against a brick wall," he said. He also said the GMC, which was alerted to the suspicions early on, could have moved faster. "It raises fundamental questions about the GMC's processes."

One patient, Brian Cunningham, was admitted to the hospital for a routine examination at the age of 79 in September 1998. Although he was frail, his stepson, Charles Farthing, said he was kept in hospital only because of bed sores. Yet six days later, he was dead.

Farthing saw him on the Monday he was admitted. He was sitting up and requesting chocolate and a box of tissues.

Farthing added: "I had a phone call to say Brian was being very difficult and they had to give him something to calm him down. When I went back on Wednesday, he was comatose. There was a black box attached to him with a bleeping noise, pumping in drugs." When Farthing protested, the sister on the ward said the patient needed the treatment for his pain.

Farthing was told his stepfather died of bronchial pneumonia. He later successfully argued for a post-mortem examination, but no attempt was made to ascertain drug levels in the body.

When Farthing heard about the complaints by relatives of other patients, he went to the police. "It took eight years," he said. "They came to interview me in 2006." His stepfather was one of the five patients that the coroner's jury decided had been overdosed.

The relatives and their lawyers feel that progress in their cases has been inexcusably slow. In 2002, the Commission for Health Improvement, which ceased operating in 2004, found significant failings at Gosport. Mistakes included the prescription of strong painkilling drugs and sedatives without supervision or checks.

Sir Liam Donaldson, the chief medical officer, commissioned Richard Baker, professor of medical governance at Leicester University, to carry out an audit of deaths at Gosport, but that report has not been made public.